The claimEvidence A · guideline-tier
5-10 mg melatonin helps you sleep
The evidence
0.3 mg is the physiological equivalent; 5-10 mg overloads receptors → next-day grogginess + rhythm disruption.
Why the claim spreads
Sold over-the-counter in big doses in the US, feeding the 'more = stronger' intuition; most people never learn the effective dose is far smaller.